Industrial radiography is a non-destructive method for the inspection and analysis of defects in items made of, for example, glass, paper, wood or metal. This method is widely used in the aeronautical, nuclear and petroleum industries for the detection of defects in welds and texture of materials in aircraft and nuclear reactor parts and in pipe lines.
This method involves exposing a radiographic product containing a silver halide emulsion to high energy ionizing radiation, generally X or .gamma. rays. The sensitivity of the radiographic emulsions to X and .gamma. rays is due to the absorption of part of these rays by the silver halide grains, causing a secondary emission of electrons, and thereby forming an internal latent image. The radiographic product is then developed and fixed.
Unlike medical radiographic films, which are exposed through luminescent screens that re-emit visible light, films for industrial radiography do not need to be sensitive to visible light, and so are generally not color-sensitive. Films for industrial radiography are either exposed directly to ionizing radiation, or exposed through a screen that intensifies the ionizing radiation. These intensifying screens, generally made of metal, increase the proportion of the ionizing radiation that can be absorbed by the silver halide grains.
Products for industrial radiography generally use a silver halide emulsion made mostly of thick grains (cubic or other solid shape) to absorb as much of the ionizing radiation crossing the emulsion layer as possible.
Also known are films for industrial radiography comprising emulsions made of specific tabular grains such as those described, for example, in U.S. Pat. No. 4,883,748 or Patent Application EP 757,286. When a radiographic product comprising tabular grain emulsions is exposed to ionizing radiations the keeping of the latent image is impaired.